Re Variation Triggered from the Paleo-Pacific Plate Evolution: Constrains from Mo Polymetallic Deposits in Zhejiang Province, South China Mo Province

Although highly dispersed, critical Re metal has attracted lots of attention from geoscientists, the controlling factors of Re-content variation are not completely understood, especially with regards to the genetic relationship between Re-bearing Mo polymetallic deposits and plate subduction evolution. It is well documented that the South China Mo Province, in Zhejiang Province, is characterized by multi-stage Mo polymetallic mineralization associated with Paleo-Pacific plate subduction. The Xianlin Mo(Cu)–Fe deposit occurs in Western Zhejiang as porphyry mineralization or skarn mineralization between the granodiorite and limestone. Zircon U–Pb analysis of the ore-forming granodiorite yields a Concordia age of 150.8 ± 1.1 Ma. Six molybdenite samples have relatively high Re contents (128.9~155.7 ppm) and deliver a weighted mean model age of 149.6 ± 1.3 Ma. These geochronological data suggest the Xianlin polymetallic mineralization was genetically related to the granodiorite in the Late Jurassic. Moreover, a new compilation of reliable Re contents and Re–Os isotope age data in Zhejiang Province indicates a decreasing trend in Re contents of molybdenite from the Jurassic Fe-/Cu-dominated Mo mineralization stage to the Cretaceous PbZn-enriched Mo mineralization stage in the South China Mo Province. Based on previously proposed models relating tectonic, magmatic, and hydrothermal processes, it is suggested that the Jurassic Re-enriched Mo mineralization, associated with I-type granitoids, formed in a compressive setting during the low-angle subduction of the Paleo-Pacific slab, whilst the Cretaceous Re-poorer Mo/Mo–Pb–Zn mineralization, related to both I- and A-type granitoids, formed in an extensional back-arc setting triggered by the rollback of the Paleo-Pacific slab

Petrogenesis of the Early Cretaceous Aolunhua Adakitic Monzogranite Porphyries, Southern Great Xing’an Range, NE China: Implication for Geodynamic Setting of Mo Mineralization

This paper reports on whole-rock major- and trace-elemental and Sr–Nd isotopic compositions of the Aolunhua adakitic monzogranite porphyries from the Xilamulun district in the southern Great Xing’an Range, Northeast (NE) China. The high-K calc-alkaline Aolunhua monzogranite porphyries are characterized by high Sr/Y ratios (34.59–91.02), Sr (362–809 ppm), and low Y contents (7.66–10.5 ppm), respectively. These rocks also show slightly enriched Sr and Nd isotopes ((87Sr/86Sr)i = 0.7051–0.7058; εNd(t) = −2.98–0.92), with young two-stage model ages (T2DM = 0.84–1.16 Ga). Such a signature indicates that these rocks were most likely formed by partial melting of juvenile mafic lower crust. Based on equilibrium melting and batch-melting equations, we performed incompatible trace elements modeling. Low FeOT/(FeOT + MgO) values indirectly reflect these adakitic rocks were derived from an oxidizing source related to magnesian granitoids. The decreasing content of TiO2, Fe2O3, Nb/Ta ratio, and moderately negative Eu anomalies suggest that minimal fractionation of Fe–Ti oxides and plagioclase may have occurred in their evolutionary history. The result shows that the Aolunhua adakitic porphyries and coeval adakitic intrusive rocks in this area had not experienced extensive fractional crystallization and were derived from 20%–40% partial melting of lower continental crust, which was composed of ~25%–40% and 5%–20% garnet-bearing amphibolite, respectively. Integrating with rock assemblages and regional tectonic evolutionary history in this regime, high (Sm/Yb)SN (SN—source normalized data, normalized to mafic lower continental crust with Yb = 1.5 ppm and Sm/Yb = 1.87 for continental adakite) and low YbSN ratios suggest that these rocks were generated in an extensional environment related to lithospheric delamination without crustal thickening. The collision between North China and Siberian cratons around 160 Ma blocked the westward movement of the lithosphere as a result of the subduction of Pacific plate, which then led to lithospheric delamination induced by asthenospheric upwelling and underplating. Subsequently, partial melting of mafic lower crust caused by mantle upwelling resulted in the Early Cretaceous magmatic activities of adakitic rocks and associated Mo mineralization in the southern Great Xing’an Range

Determination of lead elemental concentration and isotopic ratios in coal ash and coal fly ash reference materials using isotope dilution thermal ionization mass spectrometry

The rapid expansion of coal-fired power plants around the world has produced a huge volume of toxic elements associated with combustion residues such as coal fly ash (CFA) and coal ash (CA), which pose great threats to the global environment. It is therefore crucial for environmental science to monitor the migration and emission pathway of toxic elements such as CFA and CA. Lead isotopes have proved to be powerful tracers capable of dealing with this issue. Unfortunately, up to now, few high precision lead isotope data of CFA and CA certified reference materials (CRMs) determined by using the double spike technique have been reported. Hence, to facilitate the application of lead isotopes in environmental science, it is indispensable and urgent to determine a suite of high precision Pb isotope ratios and Pb elemental contents for CFA and CA CRMs. Here, we measured lead isotope ratios from four CFA and CA CRMs using thermal ionization mass spectrometry (TIMS) combined with the Pb–Pb double spike method. Lead isotope ratios values of CRMs (GBW11124, GBW08401, GBW11125d, and JCFA-1) covered wide variation ranges from 17.993 to 19.228 for Pb/Pb, from 15.513 to 15.675 for Pb/Pb, and from 38.184 to 39.067 for Pb/Pb. Lead isotope ratios of these CRMs, except for GBW11124, show good external reproducibility (2 RSD, n = 8), which is better than 0.05% for Pb/Pb and Pb/Pb, 0.07% forPb/Pb, 0.04% for Pb/Pb, and 0.05% for Pb/Pb. The Pb concentrations of these CRMs were determined using Pb single spike method. The reproducibility (1 RSD, n = 4) of Pb elemental content wa

Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent

The petrogenesis of widespread Mid-Neoproterozoic mafic dykes is crucial for the paleographic position of the South China Block (SCB) in Rodinia supercontinent and the mechanism of Rodinia breakup. Here, new detailed geochronological and geochemical data on the diabase dykes from Xide in the western Yangtze Block are presented. Zircon SHRIMP/LA-ICP-MS U-Pb dating shows that four diabase samples yield uniform crystallization age varying from 796 ± 6 Ma to 809 ± 15 Ma, while one sample gives a slight older age of 824 ± 11 Ma that is overlapped with ca. 810 Ma within uncertainties. This suggests that the Xide diabase dykes emplaced at ca. 800–810 Ma and were coeval with regional bimodal magmatism (e.g., the Suxiong bimodal volcanics). The Xide diabase dykes are characterized by low SiO2 contents, high Mg# values and Cr, Ni contents, relative enrichment of light rare-earth elements, and slight depletion of high field strength elements (e.g., Nb, Ta, Zr, and Hf) and nearly constant Zr/Hf, Nb/Ta and Nb/La ratios. Our analyses indicate that the diabase was mainly produced by interaction between lithospheric and asthenospheric mantle. Moreover, the diabase samples display geochemical characteristics affinity with typical intra-plate basalts. Together with the widespread coeval bimodal magmatic suite and sedimentary records in the Kangdian Rift, we proposed that the western Yangtze Block once experienced continental rifting during the Mid-Neoproterozoic, which also occurred in other Rodinia blocks, such as Tarim, Australia and North America. In addition, the Grenville-aged magmatism records throughout SCB with the widespread Mid-Neoproterozoic rift-related magmatism and sedimentation records imply that SCB probably played a key role in the assembly and breakup of Rodinia supercontinent

Role of mantle-derived magma in genesis of early Yanshanian granites in the Nanling Range, South China: in situ zircon Hf-O isotopic constraints

Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived mag-mas were involved in granites. We carried out in this study a systematic analysis of in situ zircon Hf-O isotopes for three early Yanshanian intrusions dated at ca. 160 Ma from the Nanling Range of Southeast China. The Qinghu monzonite has very homogeneous zircon Hf-O isotopic compositions, eHf(t) =11.60.3 and O=5.40.3. In combination with whole-rock geochemical and Sr-Nd isotopic data, the parental magma of the Qinghu monzonite were likely derived from the partial melting of re-cently-metasomatized, phlogopite-bearing lithospheric mantle without appreciable crustal contamina-tion. The Lisong and Fogang granites and the mafic microgranular enclaves (MME) within the Lisong granites have a wide range of zircon Hf-O isotopic compositions, with Hf and O isotopes being nega-tively correlated within each pluton. The Lisong MMEs were crystallized from a mantle-derived magma, similar to the parental magma of the Qinghu monzonite, with small amount of crustal assimilation. The Lisong and Fogang granites were formed by reworking of meta-sedimentary materials by man-tle-derived magmas and mixing of the mantle- and sediment-derived melts to varying degrees. It is thus concluded that these two Yanshanian granites in the Nanling Range were formed associated with growth and differentiation of continental crust